Vortex Bundles Research Articles

Thermally activated flux creep in strongly layered high-temperature superconductors.

Thermal activation energies for single vortices and vortex bundles in the presence of a magnetic field parallel to the layers are calculated. The pinning considered is intrinsic and is due to the strongly layered structure of high-temperature superconductors. The magnetic field and the current dependence of the activation energy are studied in detail. The calculation of the activation energy is used to determine the current-voltage characteristic. It may be possible to observe the effects discussed in this paper in a pure enough sample.

Flux creep and flux pinning in layered high-temperature superconductors.

For a high-${\mathit{T}}_{\mathit{c}}$ layered superconductor, we study a flux creep when the magnetic field is parallel to the layers (the CU-O planes) and vortices move across them. In a homogeneous material, the pinning of vortices results from their interaction with the layered structure of the superconductor provided the vortex-lattice period is commensurate with the interlayer spacing. The flux-creep activation energy is proportional to ${\mathit{j}}^{\mathrm{\ensuremath{-}}1}$ at small currents due to a large size of the activated vortex bundle.

Vortex motion and time dependent magnetic responses in high T c superconductors

High T c superconductors are prone to thermal motion of the magnetic vortex lattice when a large macroscopic current is carried under strong magnetic fields because of their small coherence lengths and the relatively high temperatures. By measuring the magnetic relaxation process associated with such dissipation, the thermal activation energy of the vortex motion is extracted over the whole temperature range. The temperature dependence of the relaxation process can be explained by a growth of the vortex bundle volume upon the increase of temperature which is consistent with the simple collective pinning model similar to that developed by Larkin et al.

Flicker noise in thin superconducting foils

Flicker noise in superconducting foils is explained by a random modulation of the size or the number of vortex bundles moving through the foil. Both may be caused by a random modulation of pinning centers pinning the vortex bundles.